1. Field of the Invention
The present invention relates to a method of operating a rolling mill for hot-rolling and cold-rolling of flat products in one or more roll stands each having two or more rolls, wherein the roll gaps are regulated so as to correct the differential force between the drive side and the operator side of the roll stands, while compensating the adjustment value-controlled regulation of the roll gaps which corrects the bending and balancing forces.
2. Description of the Related Art
When rolling flat products, such as hot-rolled wide strip or cold-rolled strip, on tandem rolling trains or also on reversing trains, the essential requirement which determines the quality is that the strip planarity is maintained over the entire rolled strip length. In order to meet this requirement, it is necessary that all of the stands participating in the rolling process maintain parallel roll gaps which determine the geometric shape of the cross-section of the strip.
It is difficult to meet the above-described requirement because of the differential forces which occur between the individual forces on the drive side and the operator side of the rolling train. These differential forces are the result of eccentric movements during the strip travel; they produce an increase of the extension on the housing side with the higher rolling force and lead to asymmetrical strip travel and, thus, to planarity errors.
In order to avoid these disadvantages, it has already been proposed to carry out a regulation in which the occurring differential forces are continuously measured and are converted through the so-called cross modulus into extension values on the two housing sides. These extension values can be compensated by appropriate nominal position values for the two adjustment systems on the drive side and the operator side of the roll stands. Consequently, the shape of the roll gap remains uninfluenced by the eccentric strip travel.
However, this type of regulation is harmfully influenced by the unequal forces during bending of the work rolls and balancing of the back-up rolls and work rolls on the drive side and the operator side of the roll stands; the regulation is harmfully influenced by the fact that the sizes of the lever arms of these forces are uneven as a result of the displacement of the rolls and as a result of reaction forces which result from the horizontal forces at the work rolls, the back-up rolls and possibility the intermediate rolls.
Therefore, it has already been proposed to measure the effects of the different forces from balancing and bending systems and the different lever arms and to utilize the measurement results for correcting the rolling forces at the drive side and the operator side. However, not taken into consideration in this method were the above-mentioned horizontal forces which may lead, depending on their direction, to significant differential forces in the adjustment systems.
It is known from DE 30 00 187 C2 to compensate the rolling forces which can be measured on the drive and the operator side and which are produced by the roll displacement. This displacement frequently takes place at a relatively high speed and the resulting horizontal forces reach values which are close to the frictional forces occurring between the rolls. The horizontal forces are determined by assuming a constant coefficient of friction. However, it is always a requirement that the rolls are displaced relative to each other.
The present invention is based on the finding that the horizontal forces which occur even without any roll displacement require a compensation. These inner horizontal forces are due to a type of screw effect of the rolls which roll on each other without any axial relative movement. This screw-type movement is triggered by the crossing of the rolls within the housing windows of the roll stands, wherein, for example, in stands of hot-rolled wide strip finishing trains, these forces reach an order of magnitude of 500 kN (about 50 t), with the attendant disadvantageous effect on the parallelism of the roll gap which is known to rolling mill experts. In contrast to the methods described above, the conversion of the compensation values for the rolling force measurement in the housing crossbeams makes it necessary to measure the axial forces in all rolls of the roll stand.